Linear's New Dual Synchronous Step-Down DC/DC Controller

Date
01/24/2011

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Digital power system management via I2C/PMBus interface & onboard EEPROM

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I2C/PMBus Dual Synchronous Step-Down DC/DC Controller

Digital power management benefits include easier development of complex multi-rail systems, simplified ICT and board bring-up, and remote field testing. In addition system diagnostics allow users to take corrective action to prevent a failure and make field upgrades via firmware. Data center management can minimize energy usage, reduce infrastructure cost and improve the reliability and maximize system up-time. Linear Technology Corporation announces the LTC3880/-1, a dual output high efficiency synchronous step-down DC/DC controller with I2C-based PMBus interface for digital power system management. The device combines best in class analog switching regulator performance with precision mixed signal data conversion for unsurpassed ease of power system design and management, supported by the LTpowerPlay software development system with easy-to-use graphical user interface (GUI). System Architects of a Datacom, Telecom or Storage system can as many as 16 voltage rails and need a simple way to manage these individual rails with regards to their output voltage, sequencing and maximum allowable current. They also want to easily make changes to optimize system performance and to store a particular configuration for each DC/DC converter in order to simplify the design effort. In addition, there is a growing need to monitor and report on the health of these DC/DC converters remotely, in order to identify problems, take corrective action and to prevent a failure.

The LTC3880/-1 from Linear Technology does all this and more. This device is a digitally programmable dual output multiphase synchronous step-down DC/DC controller with PMBus, SMBus and I2C interface for control, real-time monitoring, reporting and management of critical point-of-load converter functions. Querying of the output voltage, current, temperature and faults, along with controlling the output sequencing and setting the operating frequency are a few of the functions that can be controlled by a host computer. The on-chip nonvolatile EEPROM is programmed with Linear's Graphical User Interface (GUI) software (Available Free of Charge), and allows for capturing of telemetry data, fault logging and storage of the configuration file.

The LTC3880/-1 allows for digital programming and read back for real-time control and monitoring of critical point-of-load converter functions. Programmable control parameters include output voltage, margining and current limits, input and output supervisory limits, power-up sequencing and tracking, switching frequency and identification and traceability data. On-chip precision data converters and EEPROM allow for the capture and nonvolatile storage of regulator configuration settings and telemetry variables, including input and output voltages and currents, duty cycle, temperature and fault logging. The LTC3880 is a digitally programmable controller for numerous functions like VOUT, current limit set point, and sequencing to name a few, but the LTC3880 has an analog feedback control loop for best loop stability and transient response. Most of the competitive alternatives have a digital control feedback loop.

The LTC3880/-1 can regulate two independent outputs or be configured for a two phase single output. Up to 6 phases can be interleaved and paralleled for accurate sharing among multiple ICs, minimizing input and output filtering requirements for high current and/or multiple output applications. An integrated amplifier provides true differential remote output voltage sensing, enabling high accuracy regulation, independent of board IR voltage drops. Applications include high current ASIC, FPGA and processor supplies in telecom, datacom, computing and storage markets.

Configurations for the LTC3880/-1 are easily saved to internal EEPROM over the device's I2C serial interface using Linear Technology's LTpowerPlay GUI-based development software. With configurations stored on-chip, the controller can power up autonomously without burdening the host processor. Default settings can be optionally configured by external resistor dividers for output voltage, switching frequency, phase and device address. Multiple designs can be easily calibrated and configured in firmware to optimize a single hardware design for a range of applications. The converter loop gain does not change as the power supply parameters are modified, so compensation remains optimized for multiple configurations. The LTC3880 features high current integrated gate drivers to drive all N-channel power MOSFETs from input voltages ranging from 4.5V to 24V, and it can produce ± 0.50% accurate output voltages from 0.5V to 5.5V with output currents up to 30A per phase over the full operating temperature range. Highest efficiency is achieved by sensing the voltage drop across the output inductor (DCR) to sense current, or an external sense resistor can optionally be used. Programmable DCR temperature compensation cancels the TC of the copper inductor to maintain an accurate and constant current limit over a broad temperature range

The device's minimum on-time of just 90nsec makes the LTC3880/-1 ideal for compact high frequency/high step-down ratio applications. Accurate timing across multiple chips and event-based sequencing allow the optimization of power-up and power-down of complex, multiple rail systems. Additional features include constant frequency current mode control with cycle-by-cycle current limit, adjustable soft start, a synchronizable switching frequency, and programmable GPIO pins to indicate part status and to provide autonomous recovery from faults. Summary of Features: LTC3880/-1

  • Dual Output Synchronous Step-Down DC/DC Controller with Strong Onboard N-Channel MOSFET Drivers
  • I2C/PMBus Compliant Serial Interface
  • Internal Nonvolatile EEPROM Memory
  • Programmable Parameters Include VOUT, ILIM, Sequencing, Margining, OV/UV Levels & Switching Frequency
  • System Management Telemetry Variables include VIN, IIN, VOUT, IOUT, Duty Cycle, VIN Range: 4.5V to 24V
  • VOUT Range: 0.5V to 5.5V
  • ±0.5% Maximum DC Output Voltage Error over the Full Operating Junction Temperature Range
  • Temperature Compensated DCR or RSENSE Current Sensing
  • PolyPhase® for up to 6 Phase Operation
  • Phase-Lockable Fixed Frequency from 250kHz to 1MHz
The LTC3880 features an onboard LDO for controller and gate drive power and the LTC3880-1 allows for an external bias voltage for highest efficiency. Both parts are available in a thermally enhanced 6mm x 6mm QFN-40 package. The extended temperature range grade is specified over a -40°C to 85°C operating junction temperature range. The industrial grade part is specified over a -40°C to 125°C operating junction temperature range. Pricing starts at $5.35 each in 1000-piece quantities. Both versions are available from stock. For more information, visit www.linear.com/3880

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